This invention relates to methods and apparatuses for erasing information from a magnetic recording medium.
One class of apparatuses for erasing information from magnetic recording media includes one or more coils which are energized to create an electromagnetic field that varies with time but is spatially uniform in the space through which the magnetic recording medium passes. The magnetic recording medium is moved on a conveyor through the field.
In one prior art type of apparatus and method for erasing magnetic recording media, the magnetic recording media is stationary in a field created by two solenoids at an angle to each other and in another type, the magnetic material is moved on a conveyor while oriented in one position as it passes through the field. If demagnetization is insufficient, after passing through in one position, the magnetic recording medium may be repositioned on the conveyor and moved through the field while oriented in another direction.
The prior art methods and apparatuses for erasing magnetic material have a disadvantage in that either the information is not sufficiently erased or it is sent through a degaussing field multiple times with different orientations, thus increasing the time required for erasing the magnetic material.
In the prior art type apparatuses for erasing information from magnetic material in which the field is created by coils at angles to each other, the process is not continuous. Manual handling of the tape is required and the erasing is done in a field which is not uniform and not parallel to the surfaces of the magnetic material.
Attempts to provide continuous motion of the magnetic material through multiple uniform fields with different orientations have faced a problem in that residence time within fields that are strong enough to adequately erase high coercive magnetic material generate so much heat because of their inefficiency they require elaborate cooling systems. Frequently, such systems require liquid cooling.